Diagnosing a lovely knocking noise

[Mezo]

Same as the 3AJ i would imagine? (same motor) download the 3AJ service manual HERE.

Mezo.

[GeoffD]

Definitely top end I would say.... camshaft, tappets

[dan3]

Thanks for the replies, I managed to download a 3yf service manual.
This auto-decompression system in the camshaft, does anyone have any experience of that failing? The manual doesn't go into much detail...

[Mezo]

I managed to download a 3yf service manual.
doesn't go into much detail...

None of the OEM manuals will go into detail as they were intended for use by trained Yammy tech`s unlike the Clymer manual which is more oriented towards the home mechanic.

Search the forum (top right) for decomp or decompression.

Mezo.

[donnybach]

Just get TDC, the play at the top lever is 0.5mm. Don’t try to measure it, it’s the minimum movement you can get as free play. Should just feel it with your fingers. The adjustment is simple, halfway down the cable to the kickstart mech. Adjuster and locknut.

Point to note- ensure the cable isn’t pulled anywhere. ( once it’s adjusted and running, give it a tug and feel what happens, it’s acting on the exhaust valve, stopping it from closing fully, making noise and running turns to sheet. Or don’t, and take my word for it).

[dan3]

Thanks for the reply donnybach, mine is a 3yf with the centrifugal decompression built into the camshaft.
I'll try to find a NOS camshaft, parts for this bike are common-ish and don't seem to cost too much

[donnybach]

. Not seen that. My docs only go up to 1989. Interesting.
Having a bitch of a time with mine. Looks like a new stator may be called for.
I seem to have a love of all things requiring maintenance constantly. If I had a dog it would have 3 legs.

[dan3]

I'm pretty much the same at the moment

[charliext1vj]

Take the tank off and run a small fuel supply as tank will make the sound bounce. Also check the top engine mount - that wont be the issue but if loose they do generate noise. It sounds like more than one noise to me? i.e. there is piston slap as well as valves - assume somewhere in the messages some one said do a compression check too? good luck

[dan3]

Piston and rings look alright, valves need a clean. Nothing really obvious.

Strange...